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Nitrogen-15 Isotope Enrichment in Benthic Boundary Layer Gases of a Stratified Eutrophic Iron and Manganese Rich Lake

Nitrogen-15 Isotope Enrichment in Benthic Boundary Layer Gases of a Stratified Eutrophic Iron and... The applicability of the natural abundance of nitrogen gas isotope ratios was used to indicate the spatial distribution of nitrogen transformations in the water column and sediment pore waters of Lake Ngapouri, a small (area 0.19 km2), monomictic, eutrophic lake in the Taupo Volcanic Zone, North Island, New Zealand. Samples were collected from the epilimnion, hypolimnion, benthic boundary layer and at 5-cm intervals from the sediment pore waters at monthly intervals for 1 year. Values of δ15N [N2] ranged from −1 to 0.28‰ in the epilimnion, −1.5 to 1.25‰ in the hypolimnion, −1.8 to 12.2‰ in the benthic boundary layer and −0.7 to 3.5‰ in sediment pore waters. Values of δ15N [N2] showed a strong seasonal pattern that was related to the loss of dissolved oxygen in the hypolimnion during seasonal stratification. Increases in 15N-enriched dinitrogen take place in the benthic boundary layer during the periods of anoxia (taken to be dissolved oxygen concentrations <6.3 μM) and may be related to abundant ammonium substrate (up to 275 μM) to support denitrification. Nitrate concentrations increased up to 36 μM with increasing duration of anoxia. We hypothesise that an alternative electron acceptor besides oxygen is required to support the nitrification needed for the production of nitrate. Iron and manganese hydroxides and oxides from material sedimenting out of the water column may have induced chemo-nitrification sufficient to oxidise ammonium in the anoxic benthic boundary layer. The nitrate formed would mostly be rapidly denitrified so that the δ15N [N2] would continue to become enriched during the presence of anoxia, as observed in hypolimnion and benthic boundary layer of Lake Ngapouri. The changes in δ15N [N2] values indicate the potential use of isotope ratios to identify and quantify potential chemo-nitrification/denitrification in the water column and sediment pore waters of lakes. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Aquatic Geochemistry Springer Journals

Nitrogen-15 Isotope Enrichment in Benthic Boundary Layer Gases of a Stratified Eutrophic Iron and Manganese Rich Lake

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References (86)

Publisher
Springer Journals
Copyright
Copyright © 2011 by Springer Science+Business Media B.V.
Subject
Earth Sciences; Geochemistry; Hydrogeology
ISSN
1380-6165
eISSN
1573-1421
DOI
10.1007/s10498-011-9143-2
Publisher site
See Article on Publisher Site

Abstract

The applicability of the natural abundance of nitrogen gas isotope ratios was used to indicate the spatial distribution of nitrogen transformations in the water column and sediment pore waters of Lake Ngapouri, a small (area 0.19 km2), monomictic, eutrophic lake in the Taupo Volcanic Zone, North Island, New Zealand. Samples were collected from the epilimnion, hypolimnion, benthic boundary layer and at 5-cm intervals from the sediment pore waters at monthly intervals for 1 year. Values of δ15N [N2] ranged from −1 to 0.28‰ in the epilimnion, −1.5 to 1.25‰ in the hypolimnion, −1.8 to 12.2‰ in the benthic boundary layer and −0.7 to 3.5‰ in sediment pore waters. Values of δ15N [N2] showed a strong seasonal pattern that was related to the loss of dissolved oxygen in the hypolimnion during seasonal stratification. Increases in 15N-enriched dinitrogen take place in the benthic boundary layer during the periods of anoxia (taken to be dissolved oxygen concentrations <6.3 μM) and may be related to abundant ammonium substrate (up to 275 μM) to support denitrification. Nitrate concentrations increased up to 36 μM with increasing duration of anoxia. We hypothesise that an alternative electron acceptor besides oxygen is required to support the nitrification needed for the production of nitrate. Iron and manganese hydroxides and oxides from material sedimenting out of the water column may have induced chemo-nitrification sufficient to oxidise ammonium in the anoxic benthic boundary layer. The nitrate formed would mostly be rapidly denitrified so that the δ15N [N2] would continue to become enriched during the presence of anoxia, as observed in hypolimnion and benthic boundary layer of Lake Ngapouri. The changes in δ15N [N2] values indicate the potential use of isotope ratios to identify and quantify potential chemo-nitrification/denitrification in the water column and sediment pore waters of lakes.

Journal

Aquatic Geochemistry – Springer Journals

Published: Jul 12, 2011

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